Molecular sieves are classified by the Structure Commission of the International Zeolite Association according to the rules of the IUPAC Commission on Zeolite Nomenclature. According to this classification, framework type zeolites and other crystalline microporous molecular sieves, for which a structure has been established, are assigned a three letter code and are described in the Atlas of Zeolite Framework Types, Sixth Revised Edition, Elsevier (2007).
One known molecular sieve for which a structure has been established is the material designated as LEV, which is a molecular sieve characterized by having 496583 heptadecahedral cavities, to which LEV-type zeolites owe their large micropore volume (about 0.3 cm3/g), although this structure has only small 8-membered ring pore openings (4.8 Å×3.6 Å). Small pore zeolites are of importance because they exhibit zeolite-specific shape selectivity for catalytic applications. In particular, such small pore zeolites having large micropore volumes are attractive due to their large adsorption capacities. Examples of LEV-type zeolites include LZ-132, NU-3, RUB-50, ZK-20 and ZSM-45.
Synthetic zeolites are often prepared from aqueous hydrothermal reaction mixtures (or synthesis mixture(s)/synthesis gel(s)) comprising sources of appropriate oxides. Organic structure directing agents can also be included in the hydrothermal reaction mixture for the purpose of influencing the production of a zeolite having the desired structure. In some cases, the formation of the zeolite requires very long crystallization times.
An alternative approach to conventional zeolite synthesis is interzeolite conversion, i.e., the hydrothermal conversion of one zeolite into another zeolite. In an article entitled “FAU-LEV interzeolite conversion in fluoride media”, Microporous Mesoporous Mater. 138 (2011) 32-39, T. Sano et al. describe the interzeolite conversion of FAU-type zeolites into LEV-type zeolites using choline hydroxide and 1-adamantanamine as structure directing agents under hydrothermal reaction conditions. Shortened crystallization time was observed over conventional hydrothermal synthesis. T. Sano et al. report the preparation of pure LEV-type zeolites with SiO2/Al2O3 mole ratios ranging from 10.7 to 28.6. Attempts to produce pure LEV-type zeolites at higher SiO2/Al2O3 mole ratios were not successful.
It has now been found that LEV-type zeolites can be synthesized from FAU-type zeolites using an N-methyl quinuclidinium cation as a structure directing agent. Moreover, high-silica LEV-type zeolites (e.g., SiO2/Al2O3 mole ratio ≧30) can be prepared.